U.S. Pat. No. 4,227,199 is concerned with avoiding the problem of employee fraud, whereby one employee can insert the time card of another employee into a time clock to record entry and/or exit times for said other employee when, in fact, said other employee was absent at those recorded times.
According to U.S. Pat. No. 4,227,199, such possibility for cooperative fraud is overcome or avoided by replacing the ink-transfer ribbon of the time clock with a ribbon which transfers a colorless color-forming chemical, and wetting the time card with a liquid, evaporable coating containing a complimentary color-forming chemical which reacts with the time clock applied chemical and also reacts with a color-forming chemical present in a writing implement, such as a ball point pen, used by each employee to apply his or her signature whenever punching in or out. Thus, both the time clock data and the signature must be applied contemporaneously, before the liquid coating dries, i.e., within a few minutes of each other, to prove that each particular employee was present at the recorded entry and exit times.
While the system of U.S. Pat. No. 4,227,199 is operative in the manner indicated and for its intended purpose, it does not completely avoid the possibility of frauds. Since the time cards used in such system are conventional, untreated time cards, it is possible for the owner to punch in and sign at entry time, and to smear the colorless liquid coating with his finger so that he can write his signature a second time, below the first signature. Then a cooperative fellow employee can punch the owner's card at exit time and the earlier-applied second signature will make it appear that the owner was present at exit time. Other possibilities for fraud also exist.